Concerns about the environmental impact of combustion of fossil fuels have led to an increased interest in electric vehicles, which have several potential benefits compared to vehicles with conventional internal combustion engines, including: a significant reduction of urban air pollution, as they do not emit harmful tailpipe pollutants from the on-board source of power at the point of operation; reduced greenhouse gas emissions from the on-board source of power, depending on the fuel and technology used for electricity generation and/or charging the batteries and reduced dependency on fossil fuels with increasingly variable supply and fluctuating prices.
However, there are factors which discourage consumers from making the switch to electric vehicles. As of 2012, electric vehicles are significantly more expensive than conventional internal combustion engine vehicles and hybrid electric vehicles due to the additional cost of their lithium-ion battery pack. Another hurdle to overcome is the limited range of existing electric vehicles due to limitations in battery capacity.
WO 2010/140964 proposes one solution to the latter problem by feeding electric vehicles while driving. It discloses a system for electric propulsion of a vehicle along a road comprising electric conductors in the shape of conducting rails that may be put under voltage and located in longitudinal tracks or channels in the road. The vehicle is equipped with a current collector which during contact with the conducting rail allows for transfer of electric current between the conducting rail and the vehicle.
The stretch of road carrying the conductor conducting rails is divided into electrically separated road sections oriented in series, whereby the conducting rails are only put under voltage when a vehicle with its current collector passes the relevant road section.
In order for the current collector to make contact with the conducting rails it is mounted on suitable contact device acting as an extension between the vehicle and the conducting rails. One example of a contact device is given in WO 2011/123047, which is incorporated herein by reference. The contact device is adapted to co-act mechanically and electrically with an electric conductor put under voltage and located in a road section on which the vehicle is travelling, in order to supply electric voltage to the at least one electric motor which thereby propels the vehicle.
One drawback with the contact device proposed by the prior art is that the current collector is formed of a main portion made of electrically insulating material and a contact surface made of electrically conductive material protruding from the lower surface of the main portion. As such, the prior art proposes that the current collector makes mechanical and electrical contact with the bottom part of the track. However, since the conducting rail or track is located in the road it will be exposed to local weather conditions and tends to become filled with water during rain or covered in ice and snow during winter. Furthermore, all kinds of obstacles such as dirt, sand, stones or other debris may accumulate in the track. Although the main portion will act as a cleansing device to clear the conducting rail from debris, snow and/or ice, the electrical contact surface being located underneath the main portion may lead to poor and unreliable electrical contact, since the bottom part of the track may still be covered by debris, snow and/or ice even after clearing.
Therefore, there is a need to develop weatherproof contact devices with improved electrical contact.